# Weight Distribution Curve

Discussion in 'Stability' started by Kane24, Jul 11, 2019.

1. Joined: Jul 2019
Posts: 3
Likes: 1, Points: 1
Location: coprus

### Kane24New Member

Hi

I'm creating a calculation software. have a problem with Shear Force & Bending moments.

Buoyancy Curve is calculated correctly from Body Plan.
but i do not know how to draw Weight Distribution Curve correctly. (i did. but sounds something wrong)

in result i have wrong Shear Force & Bending moments Curves.

please see attached drawing. example 1 is more clear than example 2.

Any help is appreciated.

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2. Joined: Oct 2008
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Location: Japan

Hi Kane
Welcome to the forum. It does indeed look as if something is not correct. Since your bending moment should be zero at each end!
Just like this:

So either your conversion of the SF to moment values are incorrect or the addition of, or it could be your 'assumed' weight curve is not correct.

Thus, if you remove all the data except the weight curve, what is the area under the weight curve. Does it = the displacement at which you are investigating?
If not....that is where you must first look.

If it does, look at the buoyancy curve, does this = the displacement you are investigating?
If so....does the LCG lie in the same location as the LCB of the weight and buoyancy curve respectively?

These must be the first thing to double check.

Good luck...

3. Joined: Jul 2019
Posts: 3
Likes: 1, Points: 1
Location: coprus

### Kane24New Member

i already checked the area under weight curve. it does = the displacement.
the area of buoyancy curve ~= the displacement. (99%)

i do not care about LCG & LCB. ** this may be the key **

im calculating Weight & Buoyancy on every point along the ship. so i thought i should not care about LCG & LBC.

Should i shift the Buoyancy Curve to make LCB (center of B-curve area) standing at LCG (center of W-curve area) ?

i guess this may solve the problem.

4. Joined: Oct 2008
Posts: 7,808
Likes: 1,704, Points: 113, Legacy Rep: 2488
Location: Japan

If they don't line up, you have a trimming moment and an imbalance.
Since you can't "change" the LCG...it can only be the LCB. Thus it is an iterative (boring) process to make sure the LCB lies over the LCG. So you need to alter your buoyancy curve to match.
Tedious but very important!

5. Joined: Jul 2019
Posts: 3
Likes: 1, Points: 1
Location: coprus

### Kane24New Member

i see the error in Lightweight Distribution. center of this rectangle is not the real LCG.

now i made quick correction in data input and things went good.

im very thankful for your tip regarding LCG & LCB. Thank you Ad Hoc.

BlueBell likes this.
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